U.S. patent number 9,863,047 [Application Number 14/453,895] was granted by the patent office on 2018-01-09 for electrolysis device and refrigerator.
This patent grant is currently assigned to Toshiba Lifestyle Products & Services Corporation. The grantee listed for this patent is Kabushiki Kaisha Toshiba. Invention is credited to Yoshihiro Akasaka, Yoshihiko Nakano, Norihiro Tomimatsu, Norihiro Yoshinaga.
United States Patent |
9,863,047 |
Yoshinaga , et al. |
January 9, 2018 |
Electrolysis device and refrigerator
Abstract
An electrolysis device of an embodiment includes: an anode, a
cathode having a nitrogen-containing carbon alloy catalyst, and an
electrolysis cell having a membrane electrode assembly composed of
an electrolyte present between the anode and the cathode so that
voltage is applied to the anode and the cathode, wherein the
electrolyte is any one of acidic, neutral, or alkali, water is
produced by the electrolysis device at the cathode, when the
electrolyte is acidic, and hydroxide ion is produced by the
electrolysis device at the anode, when the electrolyte is neutral
or alkali.
Inventors: |
Yoshinaga; Norihiro (Kanagawa,
JP), Nakano; Yoshihiko (Kanagawa, JP),
Tomimatsu; Norihiro (Tokyo, JP), Akasaka;
Yoshihiro (Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba |
Tokyo |
N/A |
JP |
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Assignee: |
Toshiba Lifestyle Products &
Services Corporation (Tokyo, JP)
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Family
ID: |
46854497 |
Appl.
No.: |
14/453,895 |
Filed: |
August 7, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140339097 A1 |
Nov 20, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13408234 |
Feb 29, 2012 |
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Foreign Application Priority Data
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Mar 24, 2011 [JP] |
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2011-065541 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B
9/23 (20210101); F25D 17/042 (20130101); C25B
1/30 (20130101); F25D 2317/0411 (20130101) |
Current International
Class: |
C25B
1/30 (20060101); C25B 9/10 (20060101); F25D
17/04 (20060101); C25B 9/08 (20060101) |
References Cited
[Referenced By]
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JP |
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WO |
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WO |
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WO |
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WO 2010064555 |
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Jun 2010 |
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WO |
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Other References
Decision issued by the Korean Intellectual Property Office on Oct.
14, 2015, for Korean Patent Application No. 2012-21777, and
English-language translation thereof. cited by applicant .
Notification of the 2.sup.nd Office Action issued by the State
Intellectual Property Office of the People's Republic of China
dated Sep. 11, 2014, for Chinese Patent Application No.
201210053672, and English-language translation thereof. cited by
applicant .
Notice of Final Rejection issued by the Korean Intellectual
Property Office dated Aug. 21, 2014, for Korean Patent Application
No. 10-2012-21777, and English-language translation thereof. cited
by applicant .
Notification of Reason(s) for Refusal, issued by Japanese Patent
Office, dated Jun. 17, 2014, for Japanese Patent Application No.
2011-065541, and English-language translation thereof (8 pages
including translation). cited by applicant .
Notification of the First Office Action issued by the State
Intellectual Property Office of the People's Republic of China
dated Jan. 30, 2014, for Chinese Patent Application No.
201210053672, and English-language translation thereof. cited by
applicant .
Liu et al., "Studies of oxygen reduction reaction active sites and
stability of nitrogen-modified carbon composite catalysts for PEM
fuel cells," Electrochimica Acta. Jan. 11, 2010. cited by applicant
.
Notification of Reason(s) for Refusal issued by the Japanese Patent
Office dated Jul. 30, 2013, for Japanese Patent Application No.
2011-065541, and English-language translation thereof. cited by
applicant .
Notice of Preliminary Rejection issued by the Korean Intellectual
Property Office dated Sep. 30, 2013, for Korean Patent Application
No. 10-2012-21777, and English-language translation thereof. cited
by applicant .
Notice of Final Rejection, issued by Korean Intellectual Property
Office, dated Apr. 28, 2014, in Korean Patent Application No.
10-2012-21777 (8 pages including translation). cited by applicant
.
Cooper, "In Situ PEM Fuel Cell Electrochemical Surface Area and
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2014-165935, and English-language translation thereof. cited by
applicant.
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Primary Examiner: Thomas; Ciel P
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a division of application Ser. No. 13/408,234,
filed Feb. 29, 2012, based upon and claims the benefit of priority
from Japanese Patent Application No. 2011-065541, filed on Mar. 24,
2011; the entire contents of both of which are incorporated herein
by reference.
Claims
What is claimed is:
1. An operation method of an electrolysis device, the electrolysis
device comprising an anode, a cathode having a nitrogen-containing
carbon alloy catalyst, and an electrolysis cell having a membrane
electrode assembly composed of an electrolyte present between the
anode and the cathode, having a nitrogen-containing carbon alloy
catalyst, the method comprising: applying voltage to the anode and
the cathode having a nitrogen-containing carbon alloy catalyst,
wherein: the electrolyte is any one of acidic, neutral, or alkali;
a potential at the cathode having a nitrogen-containing carbon
alloy catalyst is lower than a hydrogen generation potential at a
cathode in which Pt is used as a catalyst; the device is operated
with a condition of that a hydrogen generation potential at the
cathode having a nitrogen-containing carbon alloy catalyst, is -0.2
to -0.7 V vs. RHE when the electrolyte is acidic or that a hydrogen
generation potential at the cathode having a nitrogen-containing
carbon alloy catalyst, is -0.2 to -0.9 V vs. RHE when the
electrolyte is neutral or alkali; and the device is operated with a
condition of that an oxygen reduction initiation potential at the
cathode having a nitrogen-containing carbon alloy catalyst is 0.88
to 0.75 V vs. RHE when the electrolyte is acidic or that an oxygen
reduction initiation potential at the cathode having a
nitrogen-containing carbon alloy catalyst is 0.94 to 0.87 V vs. RHE
when the electrolyte is neutral or alkali.
2. The method according to claim 1, wherein the electrolyte of the
membrane electrode assembly is an acidic membrane having cation
exchange ability.
3. The method according to claim 1, wherein the electrolyte of the
membrane electrode assembly is a neutral or alkali membrane having
anion exchange ability.
4. The method according to claim 1, wherein the electrolysis cell
is provided in a sealable vessel.
5. The method according to claim 1, wherein, compared to amount of
elements on surface, 0.1 atm % or more to 30 atm % or less of the
carbon in the carbon alloy catalyst is substituted with
nitrogen.
6. The method according to claim 1, wherein, compared to amount of
elements on surface, 0.1 atm % or more to 10 atm % or less of the
carbon in the carbon alloy catalyst is substituted with
nitrogen.
7. The method according to claim 1, wherein a part of the carbons
forming Sp2 hybrid orbital with each other in the carbon alloy
catalyst is substituted with nitrogen.
8. The method according to claim 1, wherein the carbon alloy
catalyst has a pyridine type nitrogen substitution.
9. The method according to claim 1, wherein the carbon alloy
catalyst has a pyrrolesubstitution, a pyridone substitution or a
combination of two.
10. The method according to claim 1, wherein the carbon alloy
catalyst has an N oxide type nitrogen substitution.
11. The method according to claim 1, wherein the carbon alloy
catalyst has a pore and 60% or more of the pore has a diameter of
20 nm or more.
12. The method according to claim 1, wherein the carbon alloy
catalyst has a specific surface area of 100 m.sup.2/g to 1200
m.sup.2/g.
13. An operation method of a refrigerator device, the method
comprising: applying voltage to an anode and a cathode, having a
nitrogen-containing carbon alloy catalyst, wherein: the
refrigerator device comprises an electrolysis device comprising the
anode, the cathode having a nitrogen-containing carbon alloy
catalyst, and an electrolysis cell having a membrane electrode
assembly composed of an electrolyte present between the anode and
the cathode having a nitrogen-containing carbon alloy catalyst; the
electrolyte is any one of acidic, neutral, or alkali; a potential
at the cathode having a nitrogen-containing carbon alloy catalyst
is lower than a hydrogen generation potential at a cathode in which
Pt is used as a catalyst; the electrolysis device is operated with
a condition of that a hydrogen generation potential at the cathode
is -0.2 to -0.7 V vs. RHE when the electrolyte is acidic or that a
hydrogen generation potential at the cathode having a
nitrogen-containing carbon alloy catalyst is -0.2 to -0.9 V vs. RHE
when the electrolyte is neutral or alkali; and the electrolysis
device is operated with a condition of that an oxygen reduction
initiation potential at the cathode having a nitrogen-containing
carbon alloy catalyst is 0.88 to 0.75 V vs. RHE when the
electrolyte is acidic or that an oxygen reduction initiation
potential at the cathode having a nitrogen-containing carbon alloy
catalyst is 0.94 to 0.87V vs. RHE when the electrolyte is neutral
or alkali.
14. The method according to claim 13, wherein the electrolyte of
the membrane electrode assembly is an acidic membrane having cation
exchange ability.
15. The method according to claim 13, wherein the electrolyte of
the membrane electrode assembly is a neutral or alkali membrane
having anion exchange ability.
16. The method according to claim 13, wherein the electrolysis cell
is provided in a sealable vessel.
17. The method according to claim 13, wherein, compared to amount
of elements on surface, 0.1 atm % or more to 30 atm % or less of
the carbon in the carbon alloy catalyst is substituted with
nitrogen.
18. The method according to claim 13, wherein, compared to amount
of elements on surface, 0.1 atm % or more to 10 atm % or less of
the carbon in the carbon alloy catalyst is substituted with
nitrogen.
19. The method according to claim 13, wherein a part of the carbons
forming Sp2 hybrid orbital with each other in the carbon alloy
catalyst is substituted with nitrogen.
20. The method according to claim 13, wherein the carbon alloy
catalyst has a pyridine type nitrogen substitution.
21. The method according to claim 13, wherein the carbon alloy
catalyst has a pyrrolesubstitution, a pyridone substitution or a
combination of the two.
22. The method according to claim 13, wherein the carbon alloy
catalyst has an N oxide type nitrogen substitution.
23. The method according to claim 13, wherein the carbon alloy
catalyst has a pore and 60% or more of the pore has a diameter of
20 nm or more.
24. The method according to claim 13, wherein the carbon alloy
catalyst has a specific surface area of 100 m.sup.2/g to 1200
m.sup.2/g.
Description
FIELD
Embodiments described herein relate generally to an electrolysis
device and a refrigerator.
BACKGROUND
Conventionally, a device utilizing an oxygen reduction reaction
based on electrolysis is developed for use in a dehumidifying
device, an oxygen concentration device, a de-oxygenation device, a
salt electrolysis device, a gas sensor or a humidity sensor. For an
anode of an electrolysis cell for performing the electrolysis,
catalyst of platinum, lead, oxides, iridium composite oxide, or
ruthenium composite oxide is used while a platinum based catalyst
is used for a cathode.
However, for an oxygen reduction reaction, when the voltage applied
to a cathode is higher than the theoretical voltage for generating
hydrogen, hydrogen is generated at the cathode. For example, when a
de-oxygenizing device is used for a refrigerator, a hydrogenation
reaction occurs to lower power efficiency. This is due to the fact
that Pt has a very high catalytic activity, and therefore easily
causes a hydrogenation reaction accompanied with an oxygen
reduction reaction. Further, lowering the voltage for electrolysis
has a problem that a high electric current cannot be extracted,
thus the deoxygenation efficiency is low.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an exemplary chemical structure of
nitrogen-substituted carbon of an embodiment of the invention;
FIG. 2 is a conceptual diagram of a cathode of an embodiment of the
invention;
FIG. 3 is a conceptual diagram of an electrolytic device of an
embodiment of the invention;
FIG. 4 is a conceptual diagram of a soda electrolysis device of an
embodiment of the invention, wherein a gas diffusion electrode is
included in the electrolysis device;
FIG. 5 is a conceptual diagram of a device having the electrolysis
device of an embodiment of the invention;
FIG. 6 is a conceptual diagram of a device having the electrolysis
device of an embodiment of the invention;
FIG. 7 is a conceptual diagram of a deoxygenation device of an
embodiment of the invention;
FIG. 8 is a conceptual diagram of a refrigerator of an embodiment
of the invention;
FIG. 9 is a conceptual diagram of a cell of a triode rotating ring
disc electrode of an embodiment of the invention;
FIG. 10 is a graph illustrating the XPS measurement result of
Example 1; and
FIG. 11 is a graph illustrating the XPS measurement result of
Example 1.
DETAILED DESCRIPTION
The electrolysis device of an embodiment includes an anode, a
cathode having a nitrogen-containing carbon alloy catalyst, and an
electrolysis cell having a membrane electrode assembly composed of
an electrolyte present between the anode and the cathode so that
voltage is applied to the anode and the cathode, wherein the
electrolyte is any one of acidic, neutral, or alkali, water is
produced by the electrolysis device at the cathode, when the
electrolyte is acidic, and hydroxide ion is produced by the
electrolysis device at the anode, when the electrolyte is neutral
or alkali.
Embodiments of the invention will be described below with reference
to the drawings.
The electrolysis device of an embodiment includes an anode, a
cathode having a nitrogen-containing carbon alloy catalyst, and an
electrolysis cell having a membrane electrode assembly composed of
an electrolyte present between the anode and the cathode so that
voltage is applied to the anode and the cathode.
The electrolysis device cell has a power source for applying
voltage to an anode and a cathode so that electrolysis of water
occurs at the cathode and the oxygen reduction occurs at the
cathode by using the proton generated. In general, Pt is used as a
catalyst for electrolytic oxygen reduction. However, in the cathode
of the electrolysis cell of an embodiment of the invention, Pt
having high oxygen reduction initiation potential is not included.
When Pt is included in the cathode, the oxygen reduction reaction
may easily occur as it has high oxygen reduction initiation
potential. Specifically, based on the normal hydrogen electrode
(NHE) potential, it is about 0.95 to 1.0 V vs. NHE compared to
standard electrode potential for oxygen reduction of 1.23 V vs.
NHE. However, since a cathode including Pt, which is also an
excellent catalyst for generating hydrogen, has high hydrogen
generation potential, a difference between the oxygen reduction
initiation potential and hydrogen generation potential is small. As
a result, hydrogenation reaction may also easily occur at the
cathode. Specifically, when the standard hydrogen generation
potential in acidic condition is 0 V vs. NHE, and the cathode is 0
V or less vs. NHE, hydrogen is immediately generated. Considering
the use of an electrolysis cell of an embodiment of the invention
other than a fuel cell, a high hydrogen-generating ability cannot
be an advantage.
In case of a dehumidifying device or de-oxygenating device, etc.,
voltage is applied from the outside, and therefore when power
consumption is above a certain level, a catalyst generating less
hydrogen than the oxygen reducing performance at Pt level under
electrolytic condition is advantageous. In particular, when
potential of each electrode, i.e., an anode and a cathode, is not
monitored, over-voltage ratio between each electrode cannot be
easily known as it is determined by an activity of a catalyst or
diffusion rate of materials at the anode and cathode. As a result,
generation of hydrogen cannot be known from the voltage applied
(i.e., applied voltage) only. For such case, a catalyst which
hardly generates hydrogen can provide a high threshold application
voltage, and therefore allows more efficient progress of the oxygen
reduction reaction.
Carbon without any nitrogen (for example, Ketjen Black (registered
trademark) or Vulcan (registered trademark) XC72R) has oxygen
reduction initiation potential of 0.7 to 0.6 V vs. RHE, based on
the reversible hydrogen electrode (RHE) potential, exhibiting not
so high oxygen reducing ability. The hydrogen generation potential
is about -0.1 to -0.2 V vs. RHE, indicating not so small hydrogen
generating ability. Thus, the operative potential window ([oxygen
reduction initiation potential]-[hydrogen generation potential]) is
about 0.8 to 0.9 V, and both the oxygen reducing ability and
hydrogen generating ability are not suitable for a catalyst for a
cathode of an embodiment of the invention.
As a catalyst used for the cathode of the electrolysis cell of an
embodiment of the invention, a catalyst which can cause the oxygen
reduction at a relatively fast reaction rate and has a high
activity of suppressing hydrogen generation is used.
The carbon alloy catalyst related to an embodiment of the invention
is a compound having a group of carbon atoms as a main component,
wherein a part of the carbon atoms is substituted with a nitrogen
atom. The catalyst includes an amorphous or sp3 carbon as it
overall has conductivity or high specific surface area. However,
the nitrogen is included in the skeleton of sp2 carbon atom to
substitute a carbon atom with a nitrogen atom in at least one form
of a pyridine type (A), a pyrrolepyridone type (B), an N oxide type
(C), and a tri-coordinate type (D), as shown in the structure of
FIG. 1. (A) to (D) of FIG. 1 represents an example of the
substitution with nitrogen, and the structure of FIG. 1 does not
indicate the carbon alloy catalyst itself of an embodiment of the
invention.
The nitrogen substitution quantity in the carbon alloy catalyst of
an embodiment of the invention is 0.1 atom % or more to 30 atom %
or less compared to an amount of elements on surface in the carbon
alloy catalyst. When the nitrogen substitution quantity is lower
than the lower limit, an effect expected from nitrogen substitution
is not enough, and therefore undesirable. On the other hand, when
the nitrogen substitution quantity is higher than the upper limit,
the structure is disrupted to lower conductivity, and therefore
undesirable. Further, the nitrogen substitution quantity is more
preferably in the range of 0.1 atom % or more to 10 atom % or less
from the viewpoint of conductivity. When the carbon alloy catalyst
is used as a catalyst for a cathode, hydrogen generation potential
decreases depending on the nitrogen substitution quantity and
operative potential window is more than 1 V, and therefore
desirable. Specifically, the carbon alloy catalyst is observed to
have an oxygen reduction initiation potential of 0.84 V vs. RHE,
hydrogen oxidizing voltage of -0.46 V, and potential window of
about 1.3 V, which is broader than that of Pt.
With regard to the definition of the carbon alloy catalyst as used
herein, a part of carbons forming sp2 hybrid orbital is substituted
with nitrogen is indicated.
In the carbon alloy catalyst of an embodiment of the invention, the
number of active sites in the catalyst increases in accordance with
an amount of carbon added with nitrogen. Further, as the carbon
catalyst of an embodiment of the invention has more active sites
contributing to oxygen reduction current as the surface area of the
catalyst increases, the carbon catalyst with larger specific
surface area is preferable.
Meanwhile, when the specific surface area of the carbon alloy
catalyst is too large, ratio of fine pores with a diameter of 10 nm
or less increases on the surface of the carbon alloy catalyst.
Because such fine pores lower the diffusion rate of an oxygen gas
required for oxygen reduction reaction to an extremely slow level,
they are undesirable. Thus, it is preferable that the ratio of fine
pores is small and most (60% or more) pores of the carbon alloy
catalyst have a diameter of 20 nm or more. Based on the above, the
specific surface area of the carbon alloy catalyst is from 100
m.sup.2/g or more to 1200 m.sup.2/g or less.
The substitution quantity of nitrogen atom indicates a ratio of
carbon (C) to nitrogen (N), i.e., (C/N ratio), that can be measured
by X-ray photoelectron spectroscopy (XPS). The C/N ratio can be
calculated from the ratio of signal strength of carbon atom C1s
near 290 eV and signal strength of nitrogen atom N1s near 400 eV.
C/N ratio can be calculated by using a compound having definite
composition ratio such as C.sub.3N.sub.4 as a reference
material.
A sample for measurement can be produced by carving from a cathode
of an electrolysis cell.
However, according to the measurement by XPS, a non-substituted
nitrogen such as amine is also detected, in addition to the
nitrogen which substitutes sp2 carbon. Thus, to exclude an effect
of a non-substituted nitrogen, the sample prepared is calcined for
1 hour at 800.degree. C. under argon atmosphere to dissociate a
non-substituted nitrogen, and XPS measurement is carried out
thereafter so as to remove an effect of a non-substituted
nitrogen.
Herein, further classification of substitution type can be also
made. By classifying the peaks of the signal of nitrogen atom N1s
near 400 eV, classification into 398.5 eV--pyridine type, 400.5
eV--pyrrolepyridone type, 401.2 eV--tricoordinate type, and 402.9
eV--N oxide type, and consequently the substitution type and
quantity of nitrogen can be clearly determined.
In order to specify the nitrogen substitution quantity, it is
useful that a sample produced in single-batch is divided into four
portions considering non-uniformness during heating or mixing of a
sample, and each is subjected to determination of a surface state
by XPS. Such procedure is effective for checking the quality.
[Method for Producing Carbon Alloy Catalyst]
A method for producing the carbon alloy catalyst of an embodiment
of the invention is exemplified below, but it is not limited
thereto. The carbon alloy catalyst can be produced according to a
method well known in the art including the method exemplified
below.
A resin containing nitrogen and a compound containing metal are
heat-treated under inert gas atmosphere (nitrogen and argon, etc.)
for carbonization. The carbonized product is subjected to an acid
treatment to give the carbon alloy catalyst of an embodiment of the
invention.
A resin and a compound containing metal are heat-treated under
nitrogen atmosphere for carbonization. The carbonized product is
subjected to an acid treatment to give the carbon alloy catalyst of
an embodiment of the invention. A resin containing metal can be
also used instead of a resin and a compound containing metal.
According to nitrogen plasma treatment of carbon, the carbon alloy
catalyst of an embodiment of the invention is produced.
According to chemical deposition of a material having a carbon
source and a nitrogen source, the carbon alloy catalyst of an
embodiment of the invention is produced.
Examples of the resin containing nitrogen include a phenol resin
containing nitrogen, an imide resin, a melamine resin, a
benzoguanamine rein, an epoxy acrylate resin, a urea resin,
bismaleimide aniline, a benzoxazine resin, and the like.
Examples of the metal include iron, cobalt, and the like.
Examples of the compound containing metal include compounds such as
iron phthalocyanine, cobalt phthalocyanine, iron sulfate, cobalt
sulfate, iron chloride, cobalt chloride, cobalt sulfate, iron
nitrate, potassium hexacyanoferrate, cobalt nitrate, and cobalt
acetate.
Examples of the material containing a carbon source include
methane, ethane, acetylene, ethylene, ethanol, methanol, and the
like.
Examples of a target containing a nitrogen source include ammonia,
nitrogen trifluoride, hydrazine, and the like.
Further, when the carbon alloy catalyst has low surface area or low
conductivity, it is also possible that the catalyst is supported on
a carrier or mixed with a carrier.
Examples of the support that can be used include commercially
available carbon such as Ketjen Black, Vulcan XC72R, VGCF, etc., a
carbonized organic matter containing carbon such as phenol, and a
conductive oxide such as RuO.sub.2 and IrO.sub.2.
A method for mixing a resin containing nitrogen or a resin
containing a metal and nitrogen and a metal or a compound
containing a metal include a wet and a dry mixing method which uses
a ball mill or a stirrer.
When nitrogen is introduced into carbon by carbonization, materials
such as a resin are calcined under atmosphere of gas containing
nitrogen. If there is no need to introduce nitrogen into carbon by
carbonization, materials such as a resin can be calcined under the
atmosphere of an inert gas. Temperature for carbonization is, for
example, from 600.degree. C. or more to 1200.degree. C. or less,
and the carbonization is carried out between several minutes and
several hours.
Nitrogen can be also introduced into carbon by a nitrogen plasma
treatment of carbon. Carbon can be further introduced by nitrogen
plasma treatment of the carbon alloy catalyst.
Further, if a metal compound is present after production according
to the above method, it is eliminated by a treatment with an acid.
Types of the acid used for an acid treatment may vary depending on
the metal to be used, but the examples thereof include hydrochloric
acid, sulfuric acid, nitric acid, and the like.
As for the acid treatment, the examples include that immersion in a
solution (0.1 to 10 M) diluted with pure water is carried out for
30 to 20 hours and filtration washing with pure water is repeated
three times or more.
[Cathode]
The cathode of an embodiment of the invention is constituted with,
as shown in the conceptual diagram of FIG. 2, the electrode support
material 3 and the carbon alloy catalyst 1 fixed on the electrode
support material 3 via the ion conducting binder 2. Constitution of
the cathode is not specifically limited if the carbon alloy
catalyst is fixed on the electrode support material.
When the carbon alloy catalyst of an embodiment of the invention is
dispersed in a solvent to give a slurry and the slurry obtained is
coated on an electrode support material followed by treatment such
as drying or calcination, an electrode can be produced as a
cathode. It is also possible that both the drying and calcination
are carried out. It is preferable that, before or after calcination
or drying, an ion conducting binder is added dropwise or coated.
The ion conducting binder may be admixed with a slurry. Treatments
of coating, drying and calcination can be repeated several
times.
Further, in case of using an acidic electrolyte, it is preferable
to use a proton conducting binder such as Nafion. In case of using
neutral alkali electrolyte, it is preferable to use an alkali
conducting binder.
Examples of the electrode support material include porous materials
that are the same as the gas diffusion layer used for various
electrolyte membranes and fuel cells, etc. (for example, a porous
material such as carbon paper), titan mesh, SUS mesh, nickel mesh,
and the like.
Examples of the solvent that is used for production of the slurry
include those used for producing an electrode catalyst for a fuel
cell, and the like. Specific examples thereof include, water,
ethanol, isopropyl alcohol, butanol, toluene, xylene, methyl ethyl
ketone, acetone, and the like.
As one of examples of the ion conducting binder, a fluorine-based
or hydrocarbon-based ionomer as a proton conductor and an ionomer
having an ammonium base as a hydroxide ion conductor are included.
It is preferably dissolved in a solvent such as ethanol and
used.
[Anode]
The anode of an embodiment of the invention can be produced by
using a catalyst for anode and the same materials and method as
used for producing the cathode. Examples of the catalyst used for
an anode include platinum, lead oxide, iridium composite oxide,
ruthenium composite oxide, and the like. Examples of a method for
producing the catalyst include a pyrolysis, a sol-gel method, a
complex polymerization, and the like.
Further, examples of the composite metal oxide include at least one
of Ti, Nb, V, Cr, Mn, Co, Zn, Zr, Mo, Ta, W, Tl, Ru and Ir.
Examples of the electrode support element for the catalyst include
a valve metal such as Ta and Ti.
[Electrolyte]
Examples of an electrolyte that can be used in an embodiment of the
invention include a liquid electrolyte, a cation exchange membrane,
and an anion exchange membrane, and the like. Examples of the
liquid electrolyte include sulfuric acid, nitric acid, hydrochloric
acid, an aqueous solution of sodium hydroxide, an aqueous solution
of potassium hydroxide, an aqueous solution of potassium chloride,
and the like. Examples of the cation exchange membrane include
Nafion 112, 115, 117, Flemion, Aciplex, Gore and Select. Examples
of the anion exchange membrane include A201 (trade name,
manufactured by Tokuyama Corp.). Further, a hydrocarbon-based
membrane can also be used as an electrolyte.
[Electrolytic Reaction]
When an acidic material is used as an electrolyte, a reaction as
follows (Reaction formula 1-2) occurs at an anode and a cathode,
respectively, upon the application of voltage.
Anode 2H.sub.2O.fwdarw.O.sub.2+4H.sup.++4e.sup.- (Reaction formula
1)
Cathode O.sub.2+4H.sup.++4e.sup.-.fwdarw.2H.sub.2O (Reaction
formula 2)
When oxygen supply is insufficient as surface of a cathode is
covered with water, etc. and an applied voltage is greater than a
certain value (hydrogen generating potential), the following
reaction (Reaction formula 3) also occurs at the cathode.
2H.sup.++2e.sup.-.fwdarw.H.sub.2 (Reaction formula 3)
When a neutral or an alkali material is used as an electrolyte
(electrolysis liquid), the following reaction (Reaction formula 4
and 5) occurs at an anode and cathode, respectively, upon the
application of voltage.
Anode O.sub.2+2H.sub.2O+4e.sup.-.fwdarw.4OH.sup.- (Reaction formula
4)
Cathode 4OH.sup.-.fwdarw.O.sub.2+2H.sub.2O+4e.sup.- (Reaction
formula 5)
When oxygen supply is insufficient as surface of a cathode is
covered with water, etc. and an applied voltage is greater than a
certain value (hydrogen generating potential), the following
reaction (Reaction formula 6) also occurs at the cathode.
2OH.sup.-.fwdarw.O.sub.2+H.sub.2+2e.sup.- (Reaction formula 6)
[Membrane Electrode Assembly]
As shown in part of the electrolysis cell in the conceptual diagram
of FIG. 3, the membrane electrode assembly 19 of an embodiment of
the invention includes the solid polymer electrolyte 13 between the
anode 12 and the cathode 14. Presence of the membrane electrode
assembly 19 allows close contact between the two electrodes
according to hot press or direct coating of the solid polymer
electrolyte 2 on both surfaces thereof.
[Electrolysis Cell and Electrolysis Device]
The electrolysis device 10-1 of an embodiment of the invention has,
as shown in the conceptual diagram of FIG. 3, the membrane
electrode assembly 19 described above, an electrolysis cell
consisting of the water supply tube 15, the water discharge tube
16, the air supply tube 17, and the air discharge tube 18, and the
power source 11 (power source of direct current) which applies
voltage to the two electrodes of the membrane electrode assembly
19. As the water supply tube 15, the water discharge 16, the air
supply tube 17, and the air discharge tube 18 are the members for
supplying a gas or water (aqueous solution) required for the
reaction described above, they may have any constitution depending
on types of an electrolyte or purpose and use of an electrolysis
cell. The reaction is allowed to progress by applying voltage to
the electrolysis cell.
The carbon alloy catalyst of an embodiment of the invention can be
used as an oxygen reduction catalyst having an effect of
suppressing hydrogen generation. Use of the catalyst is not limited
to a deoxygenization element or a humidifying/dehumidifying
element. It can be also used as a cathode for soda electrolysis,
for example.
Further examples of the electrolysis device of an embodiment of the
invention include the soda electrolysis device 10-2 shown in the
conceptual diagram of FIG. 4 and a chlorine generation device. A
slurry containing a mixture of the carbon alloy catalyst and a
binder (PTFE) in ethanol is coated on a titan mesh, which is then
calcined at 300.degree. C. under Ar atmosphere to give a gas
diffusion electrode, i.e., the cathode 14. For the anode 12, a
carbon electrode, etc. is used and an aqueous solution of NaCl is
used as an electrolysis liquid. The cathode 14 and the anode 12 are
separated from each other by the ion exchange membrane 13. At the
cathode side of the device shown in FIG. 4 has a constitution that
oxygen or air is supplied from the gas supply tube 17C, water is
supplied from the water supply tube 15C, caustic soda is discharged
via the liquid discharge tube 16C, and gas is discharged via the
gas discharge tube 18C. The anode side of the device shown in FIG.
4 has a constitution that an aqueous solution of sodium chloride is
supplied from the liquid supply tube 15A and chlorine gas is
discharged via the gas discharge tube 18A. When voltage is applied
between the electrodes from the external power source 11 by using
the device explained above, chlorine gas and sodium hydroxide are
generated at the anode and the cathode, respectively. By using
nitrogen-substituted carbon for such reaction, generation of
hydrogen caused by application of high voltage can be suppressed
more compared to a case in which other catalysts are used. It is
also effective in that needs for having a device for treating
hydrogen or a safety device is either lowered or eliminated or
current extraction can be efficiently carried out even when an
electrode potential is not monitored.
[Electrolysis Device Having Membrane Electrode Assembly]
By having a membrane electrode assembly connected with a power
supply of an embodiment of the invention in a vessel, an oxygen
reduction device, an oxygen concentration device, a humidifying
device or a dehumidifying element can be provided.
As shown in the conceptual diagram in FIG. 5, in the device 20-1
the membrane electrode assembly 19 is fixed so as to divide a space
within the vessel 22 to an anode side and a cathode side of the
membrane electrode assembly 19. It has a constitution that the
power supply 11 is connected to the membrane electrode assembly 19
and voltage is applied to both electrodes of the membrane electrode
assembly. Fixing of the membrane electrode assembly is secured by
the sealing agent 21 which separates the reaction space of one
electrode from that of the other electrode. Further, as shown in
the conceptual diagram of the device 20-2 in FIG. 6, the vessel 22
may be attached on the anode side or the cathode side of the
membrane electrode assembly. In the device 20-1 and device 20-2, it
is also possible that the vessel 22 and the membrane electrode
assembly 19 may be semi-fixed so that they can be detached
later.
According to a membrane electrode assembly which uses an acidic
electrolyte, a reaction of dissociating water into oxygen and
proton occurs in a space on an anode side, and therefore it can
function as a device for concentrating oxygen or a dehumidifier.
Meanwhile, in a space on a cathode side of an electrolysis cell
which uses an acidic electrolyte, a reaction of producing water
from oxygen and proton generating from an anode occurs, and
therefore it can function as a device for reducing oxygen or a
humidifier. Meanwhile, when a neutral or alkali electrolyte is
used, water is consumed at an anode while it is newly generated at
a cathode, showing an opposite function to the case in which an
acidic electrolyte is used. For a device intended for
humidification or dehumidification, it is also possible that the
vessel 22 is used as either a water supply vessel or a water
reservoir vessel, etc.
In FIG. 7, a conceptual diagram of the oxygen reduction device 20-3
using the membrane electrode assembly is shown. Electrolyte of the
oxygen reduction device 20-3 is acidic. In the oxygen reduction
device 20-3, the vessel 22 is fixed on the cathode side and the
water tank 24 is fixed on the anode side of the membrane electrode
assembly 19, both fixed by the sealing agent 21. The vessel 22 also
has the door 23 for charging and discharging any material under
reduced oxygen condition. The water tank 24 has the water supply
tube 25 and the oxygen discharge tube 26.
The vessel 22 may also have a door for introducing or removing
materials or a member such as an air suction tube, an air discharge
tube, a water supply tube, or a water discharge tube for charging
and discharging gas, liquid or other materials, etc. Such door and
tube may have any shape or function depending on purpose and use of
a device.
In addition, a device having the membrane electrode assembly can be
controlled to perform any operation of oxygen reduction, oxygen
concentration, humidification, and dehumidification by switching
between intake and discharge of gas, supply and discharge of water,
or open and close of a sealed area with an aid of a controlling
part which is not illustrated in the drawing. It is also possible
that, by having an oximeter or a hygrometer, the effect obtained
from operating device is easily identified. Further, it can be
controlled to have any oxygen concentration or humidity. The
control can be achieved either by electronic control using a
microcomputer or a programmable IC such as FPGA (Field-Programmable
Gate Array) or by manual control.
[Refrigerator Having Oxygen Reduction Device]
FIG. 8 is a conceptual diagram of the refrigerator 30 in which the
device 20' having the membrane electrode assembly is included. When
oxygen is to be reduced, the device 20' having the membrane
electrode assembly may have an embodiment that the door 23 of the
oxygen reduction device 20-3 of FIG. 8 is provided as a
refrigerator door. For reducing oxygen, although one room of the
refrigerator 30 of FIG. 8 serves as an oxygen reduction device, the
oxygen reduction device may be disposed at part of the room or it
may be disposed at any location within the refrigerator. When
oxygen reducing function is performed within a space for storing
fresh food, food oxidation can be suppressed. In the refrigerator
30, instead of the device 20' having the membrane electrode
assembly, a humidifying device or a dehumidifying device having the
membrane electrode assembly can be also used.
In addition, instead of the oxygen reduction device 20', a
controllable device to perform any operation of oxygen reduction,
humidification, and dehumidification by switching between intake
and discharge of gas, supply and discharge of water, or open and
close of a sealed area with an aid of a controlling part which is
not illustrated in the drawing can be included. It is also possible
that, by having an oximeter or a hygrometer, the effect obtained
from operating device is easily identified. Further, it can be
controlled to have any oxygen concentration or humidity. The
control can be achieved either by electronic control using a
microcomputer or a programmable IC such as FPGA (Field-Programmable
Gate Array) or by manual control.
[Test for Measuring Electrode Activity in Relation with Oxygen
Reduction and Hydrogen Generation]
As a method of evaluating characteristics of the catalyst for
reducing oxygen and generating hydrogen, potential sweep of an
electrode is considered as a convenient method. By using the cell
of a triode rotating ring disc electrode shown in the conceptual
diagram of FIG. 9, activity of an electrode in terms of oxygen
reduction and hydrogen generation is measured by potential sweep.
Specifically, at the center of FIG. 9, the operating electrode 41
is present and a reference electrode (Ag/AgCl) 42 and the opposite
electrode (carbon felt) 43 are present on the left side and the
right side of the drawing, respectively. Regarding the operating
electrode 41, a disc electrode consisting of glass fiber is formed
in the middle part and the periphery of the disc electrode is added
with a catalyst which is obtained by coating, calcining, and drying
of the catalyst ink described above. The catalyst is covered with a
polymer insulator, and the periphery of the catalyst is covered
with an Au ring electrode. Further, the periphery of the ring
electrode is covered with a polymer insulator. As for the
electrolysis liquid 44, an acidic aqueous solution (0.5 M
H.sub.2SO.sub.4 aq.) or an alkaline aqueous solution (0.1 M KOH
aq.) purged with nitrogen or oxygen was used.
With the device shown in the schematic drawing of FIG. 9, the
potential sweep is carried out at 10 mV/s by using a potentiostat.
The revolution number was fixed at 2000 rpm and the potential range
was 1.2 to -0.7 V vs. RHE.
(1) Oxidation Reduction Initiation Potential
From the voltammogram obtained by the potential sweep using an
electrolyte purged with nitrogen and oxygen for measuring electrode
activity, a difference is obtained, and the potential causing the
first appearance of a negative current is taken as an oxygen
reduction initiation potential.
(2) Hydrogen Generation Initiation Potential
Due to the generation of hydrogen from an electrolyte purged with
nitrogen and occurrence of hydrogen adsorption current, etc., exact
potential for initiating the hydrogen generation cannot be
measured. For such reasons, a potential allowing a current of -5
mA/cm.sup.2 or more under standard electrode potential is taken as
a hydrogen generation initiation potential.
(3) Production Ratio of Hydrogen Peroxide
In case of an acidic electrolysis liquid, the reaction of the
Reaction formula 2 may stop in the middle of the reaction and
hydrogen peroxide may be produced instead of water according to the
reaction of the Reaction formula 7. Thus, voltage is applied to the
gold electrode 27 of the operating electrode 21 so as to cause the
reaction of the Reaction formula 8, and as a result production
ratio of hydrogen peroxide is obtained in view of the reaction
current therefor.
Similarly, in case of a neutral alkaline electrolysis liquid, the
reaction of the Reaction formula 5 may stop in the middle of the
reaction and hydrogen peroxide may be produced instead of water
according to the reaction of the Reaction formula 9. Thus, by
allowing the reaction of the Reaction formula 10, the production
ratio of hydrogen peroxide is obtained in a similar manner.
O.sub.2+2H.sup.++2e.sup.-.fwdarw.H.sub.2O.sub.2 (Reaction formula
7) H.sub.2O.sub.2.fwdarw.O.sub.2+2H.sup.++2e.sup.- (Reaction
formula 8)
1.5O.sub.2+H.sub.2O+2e.sup.-.fwdarw.2HO.sub.2.sup.-(Reaction
formula 9) 2HO.sub.2.sup.-.fwdarw.1.5O.sub.2+H.sub.2O+2e.sup.-
(Reaction formula 10)
Specifically, 1.2 V vs RHE is applied to the gold ring electrode,
and the production ratio of hydrogen peroxide is obtained from an
electric current value during potential sweep.
Formula for obtaining the production ratio of hydrogen peroxide,
i.e., x, is as follows (Formula 1).
.times..times..times..times..times. ##EQU00001##
x: Hydrogen peroxide production ratio (%)
I.sub.R: Ring current (A)
I.sub.D: Disc current (A)
N: Collection Efficiency (-)
Further, the collection efficiency (N) is defined as the ratio
between the absolute values of the ring current and disc current,
and it was found to be N=0.4 for this case.
The collection efficiency (N) was calculated according to the
following formula (Formula 2). N=|I.sub.D|/|I.sub.R| Formula 2
Herein below, the electrolysis cell, device, and refrigerator of an
embodiment of the invention are more specifically explained with
reference to the Examples.
Detection of hydrogen generation based on MEA was made in view of
the hydrogen concentration in a gas discharged by a pump and the
hydrogen concentration in a sealed vessel, which are measured by
using a hydrogen gas detector.
Further, the theoretical oxygen consumption amount (N.sub.O2) was
calculated from the following formula (Formula 3).
.times..times..times..times..times..times..times. ##EQU00002##
N.sub.O2: Theoretical oxygen consumption amount (CCM)
I: Applied current (A)
n: Number of electrons reacted
F: Faraday constant
T: Temperature(K)
EXAMPLE 1
8 g of benzoguanamine resin containing nitrogen, 1 g of ferric
chloride, and 5 g of KetjenBlack (registered trademark) EC300J as a
carrier are mixed with 150 ml of THF (tetrahydrofuran). After
mixing, the mixture was refluxed for 2 hours at 80.degree. C. while
being stirred at 300 rpm using a stirrer. The solution obtained
after reflux was dried by an evaporator using a hot-water bath at
45.degree. C., and the dried product was calcined for an hour at
800.degree. C. under argon atmosphere. After calcination, the
calcined product was washed with 2 M hydrochloric acid to give the
carbon alloy catalyst. The sample produced was added in a stainless
pan (diameter 1 mm, depth 30 .mu.m) and the element analysis of the
catalyst surface was carried out by XPS (trade name: QUANTUM-200,
manufactured by PHI, X ray source/power output/range of analysis:
single crystal spectrophotometric AlK.alpha. ray/40 W/.phi.200
.mu.m). With a measurement at four points, it was confirmed that
the nitrogen substitution quantity is from 1.3 to 1.8%. The N1s
spectrum (one sample among the four samples measured) obtained was
shown in FIG. 10. Since FIG. 10 includes at least the pyridine type
(A), the pyrrolepyridone type (B), the N oxide type (C), and the
tri-coordinate type (D), the resolved peaks are shown in FIG. 11.
As a result of the peak resolution, it was found that the pyridine
type (A) has the highest intensity (FIG. 11).
To 1 ml of a dispersion medium adjusted to have water and ethanol
at 1:1 ratio in terms of weight, 10 mg of the carbon alloy catalyst
produced was added. The dispersion medium added with the carbon
alloy catalyst was dispersed for 30 min by ultrasonication to
produce a catalyst ink. 1 .mu.l of the catalyst ink was collected
using a micro pipette, and added dropwise to glassy carbon
(registered trade mark) with .PHI. of 3 mm followed by drying in an
incubator at 60.degree. C. for 30 min. After drying, 3 .mu.l of
0.05 wt % Nafion (registered trademark) ionomer was added dropwise
thereto. After drying again, an operating electrode was
produced.
By using the operating electrode produced, an electrode activity
test regarding oxygen reduction and hydrogen generation was
performed. Further, unless specifically described otherwise, the
electrode activity test was performed with the conditions described
above.
Regarding the electrode activity test of Example 1, the
electrolysis liquid used was 0.5 M aqueous solution of sulfuric
acid and the sweep rate was 10 mV/s.
From the measurement results, it was found that the oxygen
reduction initiation potential is about 0.84 V vs. RHE in Example
1. The hydrogen generation initiation potential is -0.46 V vs. RHE.
The operative potential window from the oxygen reduction to
hydrogen generation is 1.3 V. The hydrogen peroxide production
ratio is from 2 to 50%.
COMPARATIVE EXAMPLE 1
Except that the electrode activity test is carried out with an
electrode which uses Pt/C (trade name: TEK10E70TPM, manufactured by
TANAKA KIKINZOKU) instead of the carbon alloy catalyst as a
catalyst, it is the same as in Example 1.
From the measurement results, it was found that the oxygen
reduction initiation potential is about 0.98 V vs. RHE in
Comparative Example 1. The hydrogen generation initiation potential
is -0.012 V vs. RHE. The operative potential window from the oxygen
reduction to hydrogen generation is 0.992 V. The hydrogen peroxide
production ratio is from 2 to 15%.
When the carbon alloy catalyst of Example 1 is used instead of Pt
of Comparative Example 1, it was found that the oxygen reduction
initiation potential is low but the hydrogen generation initiation
potential is even lower and hydrogen generation is suppressed.
Further, the range from the oxygen reduction initiation potential
to the hydrogen generation initiation potential, i.e., the range in
which only oxygen reduction occurs, is broadened compared to the
case in which Pt is used as a catalyst as in Comparative Example 1.
For such reasons, a membrane electrode assembly wherein the carbon
alloy catalyst of Example 1 is used as a catalyst of a cathode can
be applied with higher voltage than a membrane electrode assembly
wherein Pt is used as a catalyst, and it has a potential of
allowing high electric current while suppressing hydrogen
generation.
COMPARATIVE EXAMPLE 2
Except that the electrode activity test is carried out with an
electrode which uses carbon containing no nitrogen (KetjenBlack
(registered trademark) EC300J) instead of the carbon alloy catalyst
as a catalyst, it is the same as in Example 1.
It was found that the oxygen reduction initiation potential is
about 0.7 V vs. RHE in Comparative Example 2. The hydrogen
generation initiation potential is -0.07 V vs. RHE. The operative
potential window from the oxygen reduction to hydrogen generation
is 0.77 V. The hydrogen peroxide production ratio is from 50 to
100%. Thus, it is found that the carbon alloy catalyst is essential
for a cathode for a reaction of reducing oxygen to water.
EXAMPLE 2
In Example 2, the electrode activity test was carried out by using
an alkali solution as an electrolysis liquid. Except that the
electrode is prepared without using an ionomer for producing an
operating electrode and 0.1 M aqueous KOH solution is used as an
electrolysis liquid, it is the same as in Example 1. As the
electrode was prepared without using an ionomer, the operating
electrode was carefully immersed to avoid any loss of the catalyst.
As the amplitude of the cyclic voltammogram does not change before
and after the test for evaluating electrode activity, it was
believed that the catalyst is not released in the electrolysis
liquid.
The oxygen reduction initiation potential is about 0.95 V vs. RHE
in Example 2. The hydrogen generation initiation potential is -0.61
V vs. RHE. The operative potential window from the oxygen reduction
to hydrogen generation is 1.56 V. The hydrogen peroxide production
ratio is from 2 to 50%.
COMPARATIVE EXAMPLE 3
Except that the electrode activity test is carried out with an
electrode which uses Pt/C (trade name: TEK10E70TPM, manufactured by
TANAKA KIKINZOKU) instead of the carbon alloy catalyst as a
catalyst, it is the same as in Example 2.
The oxygen reduction initiation potential is about 0.99 V vs. RHE
in Comparative Example 3. The hydrogen generation initiation
potential is -0.096 V vs. RHE. The operative potential window from
the oxygen reduction to hydrogen generation is 1.08 V. The hydrogen
peroxide production ratio is from 2 to 15%.
COMPARATIVE EXAMPLE 4
Except that the electrode activity test is carried out with an
electrode which uses carbon containing no nitrogen (KetjenBlack
(registered trademark) EC300J) instead of the carbon alloy catalyst
as a catalyst, it is the same as in Example 2.
The oxygen reduction initiation potential is about 0.93 V vs. RHE
in Comparative Example 4. The hydrogen generation initiation
potential is -0.58 V vs. RHE. The operative potential window from
the oxygen reduction to hydrogen generation is 1.41 V. The hydrogen
peroxide production ratio is from 50 to 100%. It was found that the
operative potential window is similar to that in Example 2 but the
hydrogen peroxide production ratio is very high. As such, it was
found that it is the carbon alloy catalyst of an embodiment of the
invention containing nitrogen which has a sufficient activity of
reducing oxygen to water.
The carbon alloy catalyst used as a catalyst for reducing oxygen of
an embodiment of the invention is not limited to the materials
indicated in Example 1 and 2. Examples of the carbon precursor
containing nitrogen include a nitrogen-containing phenol resin, an
imide resin, a melamine resin, a benzoguanamine resin, and the
like. Examples of the metallic compound include iron
phthalocyanine, cobalt phthalocyanine, iron sulfate, cobalt
sulfate, iron chloride, cobalt chloride, cobalt sulfate, iron
nitrate, potassium hexacyanoferrate, cobalt nitrate, and cobalt
acetate. These materials were mixed with 8 g of each resin, 1 g of
a metal precursor, and 5 g of KetjenBlack (registered trademark)
EC300J as a carrier in 150 ml of THF (tetrahydrofuran). After
mixing, the mixture was refluxed for 2 hours at 80.degree. C. while
being stirred at 300 rpm using a stirrer. The solution obtained
after reflux was dried by an evaporator using a hot-water bath at
45.degree. C., and the dried product was calcined for an hour at
800.degree. C. under argon atmosphere. After calcination, the
calcined product was washed with 2 M hydrochloric acid to give
various carbon alloy catalysts. The catalysts produced were found
to have nitrogen substitution ratio of .about.10% in the surface
according to XPS.
The oxidation reduction characteristics were evaluated after
producing an electrode using the catalyst in the same manner as in
the first embodiment of the invention. It was found that the oxygen
reduction initiation potential in an acidic electrolysis liquid is
about from 0.88 to 0.75 V vs. RHE. The hydrogen generation
potential is -0.2 to -0.7 V vs. RHE. The oxygen reduction
initiation potential in an alkali neutral electrolysis liquid is
about 0.94 to 0.87 V vs. RHE. The hydrogen generation potential is
-0.2 to -0.9 V vs. RHE. The hydrogen peroxide production ratio is
from 1 to 50%.
EXAMPLE 3
The electrolysis device 10-1 shown in the conceptual diagram of
FIG. 3 was produced and an electrolysis test was carried out. As an
anode of Example 3, titanium mesh (0.1 t.times.LW 0.2.times.SW 0.1)
obtained by etching in advance for 1 hour at 80.degree. C. with 10
wt % aqueous solution of oxalic acid was coated with a solution
prepared by adding 1-butanol to iridium chloride
(IrCl.sub.3.nH.sub.2O) to have 0.25 M (Ir). After that, it was
dried (10 min, 80.degree. C.) and calcined (10 min, 450.degree.
C.). Coating-drying-calcination was repeated five times to produce
the anode.
As a cathode of Example 3, 60 mg of the catalyst obtained from
Example 1 was dispersed in 50 cc of water. The liquid was suspended
under being boiled and stirred. The suspension obtained was applied
onto a carbon paper (trade name: TPG-H-090, manufactured by Toray
Industries, Inc., thickness of 0.28 mm and area of 12 cm.sup.2)
which has been subjected to water repellency treatment (20 wt %),
and absorption filtration was repeated at 0.09 MPa until the
filtrate becomes transparent followed by drying. To the dried
product, 2 wt % Nafion (registered trademark) solution dissolved in
ethanol was added by dropwise addition under reduced pressure (0.09
MPa), and then immersed in 4 wt % Nafion (registered trademark)
solution dissolved in ethanol. The resultant obtained after
immersion was boiled in pure water for 1 hour to give a
cathode.
As for the membrane electrode assembly of Example 3, the anode and
the cathode produced were added into each side of a polymer
electrolysis liquid Nafion (registered trademark) 112 (50 .mu.m),
and subjected to hot-press at 125.degree. C. and 0.36 MPa for 5 min
to give a membrane electrode assembly.
To an electrolysis cell that is produced by attaching the water
supply tube 15, the water discharge tube 16, the air supply tube
17, and the air discharge tube 18 to the membrane electrode
assembly above, external DC voltage is applied, and flowing current
(A), flow amount (1 CCM=1.667.times.10.sup.-8 m.sup.3/s), and the
oxygen concentration (vol %) in the air supply tube 17 and the air
discharge tube 18 were measured.
When the air amount in the air supply tube 17 is 100 CCM (oxygen
21%), the air in the air discharge tube 18 was 96.5 CCM and the
oxygen concentration was 18.1% at application current of 1 A. The
air in the air discharge tube 18 was 93 CCM and the oxygen
concentration was 15.1% at application current of 2 A. All the
results are almost the same as the theoretical values and no
hydrogen generation was observed. Further, occurrence of water on
the surface of the cathode was identified while voltage is being
applied.
COMPARATIVE EXAMPLE 5
Except that Pt/C is used as a catalyst for the cathode, it is the
same as in Example 3.
When the air amount in the air supply tube 17 is 100 CCM (oxygen
21%), the air in the air discharge tube 18 was 96.5 CCM and the
oxygen concentration was 18.1% at application current of 1 A. The
air in the air discharge tube 18 was 93 CCM and the oxygen
concentration was 15.1% at application current of 2 A. As the
catalyst of Comparative Example 5 uses Pt/C, it was estimated that
the hydrogen generation ratio is 1 to 50% at application voltage of
1.7 V. Thus, in Comparative Example 5, the oxygen reduction did not
occur as much amount as that of the hydrogen generation and also
wasteful power consumption is caused.
EXAMPLE 4
By attaching the membrane electrode assembly which has been
produced in Example 3 to an openable sealing vessel as in the
oxygen reduction device 20-3 of FIG. 7, an oxygen reduction device
was produced. When electric current is allowed to flow from the
power source 11 attached to the membrane electrode assembly, oxygen
concentration was decreased in accordance with the electric
current, as theoretically expected. Specifically, decrease in the
concentration from about 20% to about 5% was identified. Hydrogen
generation was not observed even when the voltage applied to the
membrane electrode assembly was changed to 1.7 V.
COMPARATIVE EXAMPLE 6
Except that Pt/C is used as a catalyst for a cathode, it is the
same as in Example 4. When electric current is allowed to flow from
the power source 11 attached to the membrane electrode assembly,
oxygen concentration was decreased. However, when the voltage
applied to the membrane electrode assembly was changed to 1.7 V, 1
to 20% of the reaction at the cathode was a reaction to generate
hydrogen.
Comparing Example 4 to Comparative Example 6, a difference in the
ability of suppressing hydrogen generation was found at an actual
device level. Specifically, in Comparative Example 6, the oxygen
reduction did not occur as much amount as that of the hydrogen
generation and also wasteful power consumption is caused.
EXAMPLE 5
By attaching the oxygen reduction device of Example 4 to a
refrigerator, a space having reduced oxygen can be included in a
refrigerator, for example. It was confirmed that, by running the
oxygen reduction device, the oxygen concentration was decreased in
accordance with the electric current, as theoretically expected,
i.e., from about 21% to about 10%. Because the internal oxygen
concentration can be lowered by closing the refrigerator door,
corrosion due to oxidation is suppressed, and as a result storage
life of foods can be extended.
While certain embodiments have been described, these embodiments
have been presented by way of example only, and are not intended to
limit the scope of the inventions. Indeed, the novel embodiments
described herein may be embodied in a variety of other forms;
furthermore, various omissions, substitutions and changes in the
form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *